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Overview of Reactor q 13 Experiments. Michael Shaevitz, Columbia University SAGENAP Meeting April 16,2004 Experimental challenges for reaching sin 2 2 q 13 0.01 Experiments and sites being considered Near term plans and requests.
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Overview of Reactor q13Experiments Michael Shaevitz, Columbia UniversitySAGENAP Meeting April 16,2004 • Experimental challenges for reaching sin22q13 0.01 • Experiments and sites being considered • Near term plans and requests
Nuclear reactors are a very intense sources ofνe with a well understood spectrum 3 GW ≈ 2×1021 MeV/s → 6×1020ne/s Reactor spectrum peaks at ~3.7 MeV Oscillation Max. for Dm2=2.510-3 eV2 at L = 1.7 km Look for small rate deviation from 1/r2 measured at a near and far baselines Counting Experiment Compare events in near and far detector Energy Shape Experiment Compare energy spectrum in near and far detector From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux Reactor Measurements of sin2213
Reactor Neutrino Event Signature • The reaction process is inverse β-decay followed by neutron capture • Two part coincidence signal is crucial for background reduction. • Positron energy spectrum implies the neutrino spectrum • In undoped scintillator the neutron will capture on hydrogen • More likely the scintillator will be doped with gadolinium to enhance capture Eν = Evis + 1.8 MeV – 2me nH → Dg (2.2 MeV) nmGd → m+1Gdg’s (8 MeV)
Going Beyond Previous Experiments • Need higher statistics with longer baseline (~1.5km) • Use larger detectors 25-50 ton units compared to previous 5-10 ton units • As before, use large power reactors • Probably multiple reactor sites • Reduce dominant reactor flux spectrum uncertainty • Use two detectors at near and far locations • Measure and/or reduce background rates • Go deeper underground (> 300 mwe?) • Need in situ measurements and reduction system • Passive shielding plus hermetic veto system • Reduce uncertainty in relative near to far detector efficiency and energy scale • Make two detectors as identical as possible • Cross calibrate with sources and observed events • Move far detector to near site for cross calibration ?
Use extrapolation from previous experiments to a 25 - 50 ton detector CHOOZ (5 tons), Palo Verde (12 tons), and Kamland (1000 tons) Liquid scintillator based detectors Buffer region to cut down backgrounds from PMT and cosmic rays Extensive veto with active and passive shielding Extra gamma-catcher region for improved energy reconstruction Calibration systems using sources, flashers, and lasers Improvements Low activity PMTs Improved veto/shielding system Multiple buffer regions Moveable detectors for cross calibrations Detector Design Issues
Scales of Experiments and Sensitivities small: sin22q13~0.04 • Goal: fast experiment to explore region just below Chooz limit. • Sensitivity through rate only • Example: “Double-Chooz” experiment medium: sin22q13~0.01 • Make a discovery of q13 in region of interest for the next 10 year program • Combinations with offaxis experiments (T2K and NuMI) give sensitivity to: • CP violation • The mass hierarchy • Sensitivity mainly rate but also some energy shape large: sin22q13~0.002-0.004?? • Measurement capability comparable to second generation offaxis experiments • Sensitivity mainly through energy shape distortions
Sensitivity Estimates small medium large Dm2 = 2×10-3 eV2 Ref: hep-ph/0403068
Experimental Challenges for Two Detector Disappearance Exp’s • Backgrounds Uncorrelated Backgrounds • ambient radioactivity • accidentals Correlated Backgrounds • cosmic rays induce neutrons in the surrounding rock and buffer region of the detector • cosmogenic radioactive nuclei that emit delayed neutrons in the detector eg. 8He (T1/2=119ms) 9Li (T1/2=178ms) • Relative Detector Uncertainties Acceptance Energy scale and linearity Deadtime • Detector size (fiducial volume): signal statistics and muon induced deadtime
Correlated backgrounds are highly related to cosmic ray muon rates Neutron production Isotope production High muon rates can also introduce deadtime effects in comparing the near and far det. Relative rate can be effected bkgd depth (mwe) Moutain Flat 10% 300 230 5% 400 300 2% 560 435 1% 730 570 Braidwood Daya Bay 100 t 50 t 25 t Reduce Muon Induced Backgrounds with Depth Go As Deep As You Can Double-Chooz
Reduce with veto and shielding Veto m’s and shield neutrons (Big effective depth) 98% veto (Chooz) 99.9% (x20) Uncorrelated background can be measured by swapping coincidence components Use energy shape to measure other background levels if shape is known Background Estimates and Mitigation Osc Signalfor sin22q13 = 0.05 Background scaled up by x3.6 Ref: hep-ph/0403068
Many possible high power multiple reactors sites with different characteristics Flat sites with shaft access allow placement flexibility, surface transportation and better shielding per depth Proximity to hills allow excavation of tunnels with horizontal access, detectorpositioning flexibility, and access to large depths for the far detector Challenge in getting reactor operators to agree to an experiment Groups working towards realizing a reactor oscillation experiment(s): Europe: PCC & CEA/Saclay & APC, MPI Heidelberg, TU Munchen, INFN/Bologna USA: Alabama, Argonne, Berkeley, Caltech, Chicago, Columbia, Fermilab, Kansas State, LBNL, Lousiana State, Michigan, Stanford, Tennessee, UCLA, UWash Japan: Tohoku Univ. , Tokyo M. Univ. China: IHEP,Chinese Inst. Of Atomic Energy, Tsinghua, Hong Kong, Hong Kong Chinese Also Russia (Kurchatov Inst.) and Brazil Workshops on Future Low-Energy Neutrino Experiments Paris, France June 20-21, 2004 Niigata, Japan March 20-22, 2004 Munich, Germany October 9-11, 2003 Univ.of Alabama; April 30-May 2, 2003 Worldwide Effort towards Realizing an Experiment
Double – CHOOZ Experiment (Ardennes, France) Example of small reactor q13 experiment
Experimental Goals: Statistical error = 0.4% Background error = 1% Relative detector error = 0.6% Advantages: Infrastructure exists for far site Reactor company would build near site if approved Disadvantages: Shallow near detector site (50 mwe) Deadtime = 500 ms / muon 50% Deadtime Higher cosmogenic bkgnd. Far baseline only 1km which limits sensitivity especially for low Dm2 Cost estimate: Detectors: ~ $7M Civil Construction: ~ $10M Schedule: Now : Securing approvals from agencies and company Feb. 05: If approved, complete design and put out bids May 07: Complete far detector Nov. 07: Complete near detector 1.5×10-3 eV2 sin22q13limit 2.0×10-3 eV2 3.0×10-3 eV2 1 2 3 4 5 6 7 8 9 10Exposure in Years Double – CHOOZ Experiment
Braidwood Experiment (Illinois) • 23.6 GW reactors – 7.17 GW maximum power • Flat: flexibility, equal overburden at near and far sites, surface • transportation of detectors • Favorable geology (dolomitic limestone): good for excavation, • low radioactivity (order of magnitude lower U, Th than granite) • Reactor company (Exelon) cooperative and supportive 1.8 km
Experimental Goals: Statistical error = 0.15% Background error = 0.4% Relative detector error = 0.4% Advantages: Shaft access Flat overburden gives better shielding Deep near site allows other reactor physics measurements Surface transport of detectors for cross calibration Favorable geology and low bkgnd Keep vibrant neutrino program in US with opportunities for education and outreach Disadvantages: Infrastructure costs high due to green field site Cost estimate: Civil: ~ $30M Detectors: $15M Schedule: 2005: R&D and full proposal preparation 2006: Project approval 2007: Construction 2009: Start data collection Braidwood Experiment
Daya Bay - Lingao, China Power 11.6 GWth (17.4 GWth by 2010) Overburden Near 200-300 mwe Far >700 mwe Lingao Daya Wan
Experimental Goals: Statistical error = 0.2% Background error = 0.3% Relative detector error = 0.4% Advantages: Horizontal access tunnel approach Large overburden reduces bkgnd Flexibility to change baseline Easy to service detector Cross calibration by moving detectors to near site Multiple small detectors Disadvantages: Chinese politics and approval system Multiple small detectors Cost estimate: ~ $25M Schedule: 2005: R&D, engineering design, and secure funding 2006-2007: Construction 2008: Start data collection Daya Bay Experiment
Reactor13 Cost and Schedule for Medium Reactor • Cost: Moderate Scale Project (< $50M) • Detector scale of MiniBooNE ~$8M / detector • Civil construction – Tunnels or Shafts and Halls ~$20 - 30M • Need to identify site, do engineering and develop proposal • R&D needed especially for Gd-liq.scint. and moveable detector • Schedule: • After site selection, approval process 1? year • Construction ~2 years • Start in 2008/2009? The Particle Physics Roadmap (in the US) 2000 2005 2010 (offaxis)
Summary • An optimized “medium scale” two detector reactor oscillation experiment can precisely measure or constrain sin22q13 at the 0.01 level. • The results from a reactor experiment on q13 are important for defining an oscillation program • Reactor measurements are competitive and complementary with long-baseline appearance experiments and can be combined to give better sensitivity to the mass hierarchy and CP violation • In the near term, a “medium scale” reactor oscillation program could go ahead rapidly if timely support is made available.
What we need from SAGENAP? • An endorsement of the physics goals of a reactor oscillation experiment and • Support for strong US participation and leadership in a reactor neutrino program.